Belt grinding machines



July 10, 1962 H. J. PLUMMER BELT GRINDING MACHINES 2 Sheets-Sheet 1 Filed April 28, 1960 Inventor H, I PL W R Attorney 2 Sheets-Sheet 2 v Attorney July 10, 1962 H. J. PLUMMER BELT GRINDING MACHINES Filed April 28, 1960 United States Patent 3,943,061 BELT GZNG MACS Henry James Plnmnier, Hadley Wood, Barnet, England, assignor to Bristol Siddeiey Engines Limited, Bristol,

England Filed Apr. 28, 1969, Ser. No. 25,434 Claims priority, appiication Great Britain May 1, 1959 4 Claims. (Cl. l-141) The invention relates to belt grinding machines and is particularly but not exclusively concerned with a belt grinding machine for grinding elongate workpieces having curved surfaces, for example, compressor or turbine blades. The term grinding has been used herein to include polishing.

A belt grinding machine usually has a grinding head including an abrasive belt arranged around a contact wheel which is positioned, in use, to hold the belt against the work-piece to be ground. A usual size for the contact wheel is two to three inches diameter; but with such a wheel it is not possible to grind very small radii of concave form and also it is not possible to grind close to the platforms or shrouds of turbine or compressor blades.

An attempt has been made to reduce the diameter of the contact wheel; but at the extremely high belt speed required, the rotational speed of a very small contact wheel would be of the order of 50,000 rpm. It has been found that at that speed conventional bearings, such as needle roller bearings, have a short life and are impracticable.

An object of the present invention is to provide a belt grinding machine, or a grinding head therefor, having a very small diameter contact Wheel, with which small concave radii can be ground and which will have a comparatively long life.

According to the invention, a grinding head for a belt grinding machine and of the kind including an abrasive belt, arranged to be driven around a contact wheel, which is positioned, in use, to hold the belt against a work-piece to be ground, is characterised in that the contact wheel is located, at each end thereof, in a nip between a pair of partly overlapping rotatable discs and is held in the nip by the tension of the belt, the discs being mounted in bearings and arranged for free rotation by the belt via the contact Wheel and each being of considerably larger diameter than the engaging ends of the contact wheel.

The contact wheel may additionally be held in position in the nips between the discs by a retaining arm mounted on supporting means for the discs.

The invention also includes a belt grinding machine having a grinding head according to the two immediately preceding paragraphs.

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, in which:

FIGURE 1 is a perspective view of the upper portion of a belt grinding machine, showing the grinding head according to this invention;

FIGURE 2 is a perspective View, to a larger scale, of part of the grinding head shown in FIGURE 1;

FIGURE 3 is a view in the direction of arrow III in FIGURE 2; and

FIGURE 4 is a section on the line IV-IV in FIG- URE Referring to FIGURE 1, the grinding head is shown generally by arrow 1 and includes a contact wheel 2 and an endless abrasive belt 3, which is passed around the contact wheel 2, which in use holds the belt against Bfidldbl Patented July 19, 1962 the surface of a work-piece to be ground. The belt 3 is guided by idler pulleys 4 and is driven by a pulley 5 driven by an electric motor 16.

In order to grind small radii of the order of 0.25 inch, the contact wheel 2 must be of correspondingly small diameter. If a normally supported contact wheel was of say half inch diameter, an extremely high bearing speed of 50,060 rpm. would be required as a result of the high belt speed which is necessary. According to this invention, the small diameter contact wheel 2 is mounted between two pairs of partly overlapping discs 6 and has at each end an axially extending spindle 7 which bears in the nip 8 between the two discs 6 at that end of the wheel 2. The discs 6 are of considerably larger diameter than the spindle 7 of the contact wheel 2 and are supported on stub shafts 9, extending from the sides of the discs 6 remote from the contact wheel 2, inantifriction bearings 10, e.g., ball bearings. Owing to the reduction ratio afiorded by the ratio of the diameter of the contact wheel spindle 7 to the diameters of the discs 6, the bearing speeds of the discs are reduced to a reasonable level. The abrasive belt 3 passes around the contact wheel 2 and the wheel is held in the nips 3 by the tension of the belt. No driving means are provided for the discs other than the belt acting through the contact wheel 2. A retaining arm 12 pivoted at 14 to a housing 13 for the discs 6 is positioned at each end of the contact wheel spindle 7 to support the contact wheel 2 so that should a belt breakage occur, the wheel Will not fly out of the nips 8. The housing supporting the discs and the contact wheel are formed as a unit which can be made interchangeable with a standard unit directly supporting a larger contact wheel.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. A grinding head comprising an abrasive belt, a driving wheel therefor, a contact wheel arranged to be driven by the belt, the contact wheel being positioned in use to hold the belt against a work-piece to be ground, a pair of partly overlapping rotatable discs mounted at each end of the contact wheel and forming a nip, in which the adjacent end of the contact wheel is located and is held therein by the tension of the belt, and supporting means for each of said discs providing free rotation of the disc by the belt via the contact wheel, each disc being of considerably larger diameter than the engaging ends of the contact wheel, the axes of rotation of said discs lying parallel to the axis of rotation of the contact wheel on the side thereof remote from the workpiece.

2. A grinding head as claimed in claim 1 further comprising a retaining arm mounted on supporting means for the discs and providing additional means for holding the contact wheel in position in the nips between the discs.

3. A grinding head as claimed in claim 1 in which the supporting means for each of said discs comprises a stub shaft extending axially from the disc on the side thereof remote from the belt and an anti-friction bearing for said stub shaft.

4. A belt grinding machine including a grinding head comprising an abrasive belt, a driving wheel therefor, a contact wheel arranged to be driven by the belt, the contact wheel being positioned in use to hold the belt against a work-piece to be ground, a pair of partly overlapping rotatable discs mounted at each end of the contact wheel and forming a nip, in which the adjacent end of the contact Wheel is located and is held therein by lthe tension of the belt, and supporting means for each of said discs providing free rotation of the disc by the belt Via the contact wheel, each disc being of considerably larger diameter than the engaging ends of the contact wheel, the axes of rotation of said discs lying parallel to the axis of rotation of the contact wheel on the side thereof remote firom the workpiece.

References Cited in the file of this patent UNITED v STATES PATENTS Kopczynski Sept. 2, 1958 

